.Population bottlenecks can restrict variation at functional genes, reducing the ability of populations to adapt to new and changing environments. Understanding how populations generate adaptive genetic variation following bottlenecks is therefore central to evolutionary biology. The major histocompatibility complex (MHC) is a multigene family that provides an ideal model for studying adaptive genetic variation due to its central role in pathogen recognition. While de novo MHC sequence variation is generated by point mutation, gene conversion can generate new haplotypes by transferring sections of DNA within and across duplicated MHC loci. However, the extent to which gene conversion generates new MHC haplotypes in wild populations is poorly understood. We used a 454 sequencing protocol to screen MHC variation across all 13 island populations of Berthelot’s pipit (Anthus berthelotii). The recent colonisation of this species (<75,000 years ago), along with the replicated island system gave us a unique opportunity to identify which MHC alleles were involved in the original colonisation events, and which have been generated in situ, post colonisation. This, in turn, allowed us to identify how new MHC haplotypes have been regenerated across the island populations. In light of these results, I will discuss the roles of mutation, gene conversion and selection in generating and maintaining functional genetic diversity in bottlenecked populations.

Abstracts (coauthor)

Understanding the population history of endangered species is important for interpreting contemporary ecological processes, and of conservation high importance. We use microsatellite markers and museum specimens to examine 140 years of genetic diversity change in the Seychelles warbler (Acrocephalus sechellensis), a model system for evolutionary and conservation biology. In the 1960s this species was reduced to ca 30 individuals on a single island, but it is unknown whether it has ever been widespread and abundant. Across museum and contemporary samples, we found a 25% reduction in genetic diversity, which resulted in significant genetic structure. Using simulations we show that the warbler was bottlenecked from a large, outbred population. An ancestral effective population size of over 2,000 was reduced to less than 50 within the last century, which most likely occurred due to human disturbance. The approaches used form a powerful way of inferring population history, thus helping us to understand ecological processes and inform conservation.

In several animal species, subordinate individuals forego independent breeding to assist others in raising offspring that are not their own. Several benefits underlying the evolutionary stability of such seemingly altruistic helping behaviour have been invoked, and assessment of variation in individual investment in response to variation in such benefits is often being used to reveal the adaptive significance of these benefits. In the Seychelles warbler Acrocephalus sechellensis, subordinates gain substantial fitness benefits of helping: individuals that start as helpers have higher life time fitness than subordinates that do not help initially. Nonetheless only about half of the subordinates do help. Using a range of physiological measures, we show here that helping carries a substantial cost, as helpers were in poorer condition after the breeding season than non-helping subordinates . Additionally, only individuals in good condition do provide help, because probably only these individuals can overcome the associated costs. This result suggests that, apart from the associated benefits, variation in subordinates’ condition explains part of the variation in helping behaviour. This highlights that considering the condition of the (potential) helper and the costs of helping are important to unravel the benefits of helping, and to understand the variation in the expression of helping behaviour within species.

Lower ‘visibility’ of female scientists, compared to male scientists, is a potential reason for the under-representation of women among senior academic ranks. Visibility in the scientific community stems partly from presenting research as an invited speaker at organised meetings. We analysed the sex ratio of presenters at the European Society for Evolutionary Biology Congress 2011, where all abstract submissions were accepted for presentation. Women were under-represented among invited speakers at symposia (15% women) compared to all presenters (46%), regular oral presenters (41%) and plenary speakers (25%). At the ESEB congresses in 2001–2011, 8–23% of invited speakers were women. This under-representation of women is partly attributable to a larger proportion of women, than men, declining invitations: in 2011, 50% of women declined an invitation to speak compared to 26% of men. We expect invited speakers to be senior scientists or authors of recent papers in high-impact journals. Considering all invited speakers (including declined invitations), 23% were women. This was lower than the baseline sex ratios of early–mid career stage scientists, but was similar to senior scientists and authors published in high-impact journals. High-quality science by women therefore has low exposure at international meetings, which will constrain Evolutionary Biology from reaching its full potential. We wish to highlight the wider implications of turning down invitations to speak. In particular, under-representation of women among invited speakers reduces the number of female role models for evolutionary biology students and contributes to the leaky pipeline. We encourage conference organisers to implement steps to increase acceptance rates of invited talks.

At the heart of the recent debate on sex roles lies the interpretation of the Bateman gradient, the slope of the regression of reproductive success (number of offspring, T) over mating success (number of mates, M). Typically, males are considered to have a steeper Bateman gradient, thus to undergo stronger sexual selection than females. Recent work challenges this paradigm by questioning the measurement and interpretation of Bateman gradients. In this study we combine an experimental approach with multivariate analyses to resolve the significance of male and female Bateman gradients in the red junglefowl, Gallus gallus.
First, the male Bateman gradient is measured by deducing mating success from paternity of the offspring, without accounting for matings that fail to result in fertilisation. We demonstrated that inferring M from offspring parentage leads to a 50% overestimate of the male Bateman gradient compared to a regression using fine-grain mating behaviour.
Second, while the male Bateman gradient is concerned with the causal relationship between M and T, we show that variation in other components of male reproductive success, namely female fecundity and paternity share, also cause the Bateman gradient to be overestimated of a further 69%.
Finally, there is growing appreciation that female Bateman gradients can be steeper than originally thought. We show that females display a positive Bateman gradient, suggesting that they benefit by mating with multiple males. However, an experimental test shows no evidence that productivity increases with number of mates in females, suggesting that the female Bateman gradient emerges as spurious consequence of males preferentially mating with more fecund females.
Our results demonstrate that the mechanisms underpinning Bateman gradients are more complex than currently appreciated, and that understanding the causal relationship of M and T and how it defines sex roles requires an integrated experimental approach.

Inbreeding and reduced genetic diversity are known to affect the capacity of an individual to resist pathogen infection so that a negative relationship between pathogen prevalence and heterozygosity is expected. Thus, a high susceptibility to pathogens may contribute to shorten extinction time in populations with low genetic diversity. At the range scale, peripheral populations tend to be smaller and more isolated than core populations and are generally more prone to incur the costs of reduced genetic diversity. Elevated extinction risk in peripheral populations is of particular concern for species with unfavourable conservation status. However, the relationships between census size, effective size (genetic diversity) and parasite prevalence is not straightforward because gene flow from the core may maintain genetic diversity and the ability to resist pathogens at the range periphery, even in declining populations. The Corncrake Crex crex, a short live migratory bird distributed across the Palearctic has shown rapid declines in Western Europe over recent decades while Eastern populations remained large. We analysed the relationship between genetic diversity, gene flow and avian malaria prevalence across a large part of the species range. We found a very low level of population structure and no evidence of reduced diversity in peripheral populations which was likely caused by a high dispersal across the breeding range. Furthermore, contrary to expectations, the parasite prevalence was 10 times higher in core populations compared to peripheral ones, even in areas of high bird density. Our results clearly show that decouplings may occur in periphery-core systems between census and effective population size, and between genetic diversity and pathogen prevalence. Species dispersal characteristics, population densities and the ecology of pathogen community are likely to strongly affect these relationships precluding the quick and easy forecasting of a populations fate.